1. Field of the Invention
This invention relates to a process for the production of surfactant-containing detergent or cleaning tablets using microwaves.
The disadvantage of conventional detergent or cleaning tablets, particularly detergent tablets, which are normally produced by compression molding was that these tablets did not dissolve sufficiently quickly on account of their compactness and the active substances were released too slowly in the wash cycle. In addition, detergent tablets in particular had an inadequate disintegration rate.
2. Discussion of Related Art
Earlier hitherto unpublished International patent application PCT/EP94/01330, to the disclosure of which reference is specifically made, describes in detail the production of washing- and cleaning-active tablets with an extremely high dissolving or disintegration rate using microwaves. A crucial requirement for the production of tablets from powder-form or granular raw materials using microwaves is that these starting materials should be at least partly present in hydrated form, "hydrated" meaning "hydrated under certain conditions in regard to the temperature, pressure or relative humidity of the atmosphere to which the raw material is exposed or with which the raw material is in equilibrium". By "microwaves" in the context of the invention is meant the entire frequency range from 3 to 300,000 MHz which covers not only the actual microwave range above 300 MHz, but also the radio wave range from 3 to 300 MHz. So-called macrosolids, including for example blocks in addition to tablets, which may normally contain up to 40% by weight of surfactants can be produced by this technique. If one of the raw materials used in substantial quantities is a crystalline layer silicate, more particularly of the SKS-6.RTM. type (crystalline sodium disilicate, a product of Hoechst AG, Germany), the surfactant content may even be as high as 60% by weight. Other possible ingredients are, on the one hand, the microwave-active hydrated inorganic or organic salts, such as alkali metal phosphate, alkali metal carbonate, alkali metal bicarbonate, alkali metal sulfate and citrate, and also zeolite and even peroxy bleaching agents, such as perborate or percarbonate. These are preferably used in encapsulated form.
Difficulties are still involved in the production of microwave tablets containing anionic surfactants in substantial quantities, for example in quantities above 10% by weight, and inorganic salts in quantities below 60% by weight. Although tablets such as these can be produced on an industrial scale in accordance with the teaching of PCT/EP94/01330, sulfate- and sulfonate-containing anionic surfactants in particular tend to turn brown in color in concentrations as high as these so that, although washing performance is not affected, the discoloration is not accepted by the consumer. In addition, the dissolving behavior of the tablets deteriorates with increasing surfactant content.
It has now been found that the dissolving behavior of surfactant-containing microwave tablets can be increased providing a significant proportion of the surfactants is not incorporated in the tablets as an individual raw material.